An organic electroluminescence element (to be also referred to as an “organic EL element” hereinafter) has a structure in which a pair of electrodes sandwich a thin film containing an organic electroluminescence material (to be also referred to as an “organic EL material” hereinafter). An organic EL element can control luminescence intensity by a voltage to be applied or the amount of current flowing in the element. A display device has been developed, which has a display screen formed by forming pixels using this property.
A display device using organic EL elements can display an image by individually controlling the luminescence of each pixel. This eliminates the need for the backlight required in transmissive liquid crystal display devices and hence can implement thinner display devices. In addition, since a circuit using organic EL elements and thin film transistors which drive them can be formed on an organic resin film, a flexible display device whose substrate itself has flexibility is being developed.
The flexibility of an organic EL element is a highly advantageous point as compared with other types of display devices such as liquid crystal display devices and PDP display devices. However, basically, the organic EL element has a structure simply formed by stacking organic thin films using a method like vapor deposition, which cannot ensure adhesion, and hence the adhesion strength between the thin films is weak. This may result in film peeling. For example, Japanese Patent Laid-Open No. 2011-228361 discloses organic semiconductor materials having excellent adhesion to metal thin films.